Effect of Different Herbicides On Switchgrass Establishment.

Weed competition is a major limitation for Switchgrass (Panicum virgatum L.) establishment. The objective of this experiment is to determine the effect of various herbicides to selectively remove grassy-weed competition, and improve establishment. Fields were conducted in 2007, 2008, and 2009, and a greenhouse experiment was conducted in 2009 only.  Cave-in-Rock (upland type), NFGA993 (lowland type) switchgrass, crabgrass, Johnsongrass, Texas panicum, yellow foxtail, broadleaf signalgrass were planted in the field in 2008 and 2009 on either a Eufaula loamy sand or Dale silt loam.  Forty herbicide treatments were evaluated at various timings (Pre, 2-leaf, 3-leaf, and 4-leaf) and rates.  Greenhouse experiment evaluated twenty herbicides on NFGA993 and crabgrass only in 2009 on a Dale silt loam.  The effects of various herbicides were determined by measuring switchgrass seedling count at 30 and 60 days after treatment(DAT), visual switchgrass injury and weed control at 30, 60, 90DAT, and switchgrass percent coverage at end of season.   PRE herbicides: On both loamy sand and silt loam soils, the ALS herbicides cause excessive injury with the exception of FirstRate (cloransulam), which suppresses crabgrass. At the 2-leaf stage, Atrazine, Paramount (quinclorac), Prowl H2O (pendamethalin) were safe on both upland and lowland switchgrass, and Option (foramsulfuron) was relatively safe on lowland type only.  At the 3-leaf stage, Outrider (sulfosulfuron) and Option were generally safe and controlled Johnsongrass.  Accent (nicosulfuron) at the 3-leaf stage was very effective on lowland switchgrass in controlling all grassy weeds except crabgrass in 2008, but it caused excessive injury in 2009.  At the 4-leaf stage, MSMA was effective at controlling all grassy weeds and was relatively safe on lowland switchgrass, but caused excessive injury on upland switchgrass.  Delaying applications to the 4-leaf stage generally resulted in too much completion from the grassy weeds.